Dunn, Medullated Nerve Fibers. 70 1 



Since the left leg is the one affected by the operation, we consider 

 first whether some change has occurred in that leg which has modi- 

 fied and vitiated the results. The left leg retains only afferent nerve 

 fibers. We can compare those that innervate the skin with those that 

 innervate the skin on the right or unoperated side. In Table IV we 

 find 1527 cutaneous nerve fibers for the left thigh, 1553 cutaneous 

 nerve fibers for the right thigh. In the shanks, Table V, we find, 

 curiously enough, 1078 cutaneous nerve fibers for each side. At 

 the same levels the cutaneous nerve fibers for both legs are intact. 



Comparing, Tables IX and X, the excess in the left leg of frog 

 E and that in the left leg of frog IIB we find the excess numbers 

 bear approximately the same percentage relation to the observed num- 

 bers as was found for frog IIB, but the actual numbers are much less, 

 so that a large number of efferent fibers, many of them splitting, 

 might be added to the afferent nerve fibers without surpassing the 

 numbers which might be present in the combined groups, if the 

 observed numbers for frog E were scaled to those for frog IIB. 



Eurthermore we are able to compare the findings regarding excess 

 nerve fibers on this operated side in a long stretch of the nervus 

 ischiadicus where no branches have left the main trunk, although the 

 main trunk has subdivided at the lower level. In Table III, the K. 

 ischiadicus below its branches on this left side shows 2424 nerve 

 fibers while its continuing branches, the X. tibialis and X. peroneus 

 together show 2531 nerve fibers, an increase of 107 nerve fibers or a 

 percentage increase over the nerve fibers at the upper level of more 

 than 4 per cent. In frog IIB, Table VI, we have between the same 

 levels an increase of 184 fibers in the left leg, and 210 nerve fibers 

 in the right leg, a percentage increase of about 5 per cent. The 

 left leg then seems to have suffered no change further than the loss 

 of the sectioned ventral root nerve fibers. 



Turning to the findings for the right leg of frog E, let us ascertain 

 first what this same region in the X. ischiadicus will reveal. Accord- 

 ing to Table III, the upper level, that of the X. ischiadicus below 

 the branches, shows 3452 nerve fibers, while the X. tibialis and the 

 X. peroneus together at the entrance to the shank show 3415 nerve 

 fibers, a decrease of 37 nerve fibers. That is, at this lower level in 



